Role and Mechanism of lncRNA-pvt1 in the Pathogenesis of Acute Lymphoblastic Leukemia in Children

Objective. To investigate the role and mechanism of lncRNA-pvt1 in the pathogenesis of childhood acute lymphoblastic leukemia (ALL). Methods. The expression of lncRNA-pvt1 in bone marrow tissues of ALL patients after initial diagnosis and complete remission was detected by RT-PCR to explore its possible involvement in the pathogenesis of ALL. The proliferation and apoptosis of Jurkat cells transfected with lncRNA-pvt1 were observed by MTT and flow cytometry. Results. lncRNA-pvt1 expression was upregulated in bone marrow of ALL patients. Knockdown of lncRNA-pvt1 inhibited Jurkat cell proliferation and increased its apoptosis rate. Conclusion. Silencing lncRNA-pvt1 expression can inhibit the development of ALL.


Introduction
Childhood acute lymphoblastic leukemia (CALL) is the most common malignancy in children under 14 years of age and remains one of the leading causes of death from pediatric disease despite having a 5-year EFS of more than 80% [1]. ALL is a bone marrow malignant disease that originates from a B-based or T cell abnormal proliferation of lymphocytes. The original cell proliferation can accumulate in the bone marrow and inhibit normal hematopoietic function and can also invade the macus, lymph nodes, gonad, liver, and spleen. In recent years, with the continuous improvement of clinical risk stratification, optimization of combined chemotherapy, and supportive treatment under the guidance of MICM typing, individualized and precise treatment has significantly improved the remission rate of ALL in children. However, there are still some children with poor prognosis due to insensitivity to chemotherapy or recurrence after remission [2]. Improving the prognosis of these children has become the focus of research, and exploring its molecular pathogenesis may become a new breakthrough point.
It has been found that various biological processes are determined by the regulatory potential of noncoding parts of the genome. It has been estimated that about 1.5% of the genome is responsible for protein coding, while many noncoding regulatory elements are transcribed into noncoding RNAs (ncRNAs) [3]. Long noncoding RNA (lncRNA) is a new form of ncRNA. lncRNA refers to DNA transcription products with a length of more than 200 nucleotides and generally does not participate in the protein coding process. lncRNAs were initially considered nonfunctional transcription waste, but in recent years, after a lot of studies and demonstrations, most lncRNAs have been identified as key regulatory factors in the process of transcription and translation, playing an important role in cell transcription and posttranscriptional regulation, development regulation, epigenetics, disease occurrence, and other aspects [4,5]. It has been reported that lncRNA plasmacytoma variant translocation 1 (PVT1) is associated with cell proliferation, invasion and metastasis, apoptosis, and tumor prognosis [6]. Both domestic and foreign studies have found that pvt1 expression is upregulated in patients with CML, and studies have shown [7] that pvt1 silencing leads to cell cycle arrest by negatively regulating the expression of cyclin-dependent kinase inhibitors P15 and P16, thereby inhibiting tumor cell growth. However, the role and related mechanisms of lncRNA-pvt1 in children with ALL have been rarely reported.
In this study, the expression of lncRNA-pvt1 in bone marrow cells of newly diagnosed and completely relieved patients with ALL was detected to explore the relationship between lncRNA-pvt1 and clinical features of ALL. Then, lncRNA-pvt1 was transfected into Jurkat cells, and the apoptosis of the transfected Jurkat cells was detected by flow cytometry, to explore the mechanism of lncRNA-pvt1 in the pathogenesis of childhood acute lymphoblastic leukemia, in order to find new molecular biological indicators for the early detection of ALL and disease monitoring and evaluation in the future and to provide new targets for future molecular therapy.

lncRNA-pvt1 Expression in Childhood Acute
Lymphoblastic Leukemia. Fifty CALL patients admitted to our department from January 2020 to January 2021 were selected as the study subjects, and 2-5 mL of bone marrow samples were taken from the children after initial diagnosis and complete remission. The content of lncRNA-pvt1 in bone marrow was determined by RT-PCR, and the results were analyzed by SPSS 22.0 statistical software. Lncrna-pvt1 gene expression was compared between the two groups, and P < 0:05 was considered statistically significant. The study conformed to the provisions of the Declaration of Helsinki. And the ethical approval was obtained from the ethics committee(s) of Shanxi Children's Hospital.

Expression of lncRNA-pvt1 in Human Peripheral Blood T Cells in Jurkat Model Cells Cultured
In Vitro. Jurkat model cells were cultured with human peripheral blood T cells in vitro. The cultured cells were divided into the negative control group and lncrna-pvt1 cell simulation group. Lncrna-pvt1 was transfected into Jurkat cells. The content of lncrna-pvt1 was analyzed by RT-PCR to observe the effect of transfection on the proliferation of Jurkat cells. The apoptosis of Jurkat cells transfected with lncrna-pvt1 was detected by flow cytometry, and the data were collected by SPSS 22.0 software for statistical analysis. All results were analyzed and expressed by the expression of measurement data. Different analysis results used different analysis methods. The differences between groups were observed by analysis of variance and LSD t-test. When P < 0:05, it was statistically significant.

Comparison of Basic Information between the Two
Groups. The two groups of children were compared in age, gender, course of disease, and other basic information; there was no significant difference, comparable in Table 1.

The Expression of lncRNA-pvt1 in ALL and Control
Groups. Compared with healthy people, the expression of lncRNA-pvt1 in bone marrow of ALL patients was increased ( Figure 1).

Discussion
ALL is a common malignant disease of the blood system in which the differentiation of primitive and juvenile lymphocytes is blocked due to the malignant proliferation of hematopoietic stem cells and the blocked apoptosis, which inhibits normal hematopoiesis and invades extramedullary organs. The incidence of ALL is about 0.69 out of 100000. Adult ALL accounts for 20%-30% of adult acute leukemia. Childhood ALL accounts for about 80% of acute leukemia in children. After standardized treatment, the complete response rate of adult ALL after induction chemotherapy can reach 70%-90%, and the disease-free survival rate of 3-5 years is only 30%-60% [8]. Long-term event-free survival for ALL in children can be 70% to 80%. Although the induced remission rate of ALL is high, its recurrence rate is high, and once the disease recurs, it progresses rapidly and has a high mortality rate. Therefore, it is imperative to study the pathogenesis of ALL.
Recent studies have shown that as small molecules with multiple biological functions, miRNA and lncRNA have played an extremely important role in the progression of a variety of tumors and become a research hotspot in the field of tumors [9]. There are many studies on the mechanism of tumor caused by miRNA, but the relationship between lncRNA and tumor pathogenesis is still not very clear. Existing studies have shown that lncRNA is powerful because of its wide variety and has become an important signal molecule in various regulatory mechanisms. lncRNA refers to a loosely structured RNA transcript with more than 200 nucleotide units, which has no protein coding potential [10]. Recent studies have shown that lncRNA can be used as a biomarker for diagnosis, treatment response, and prognosis of CALL.. Similar to protein coding transcripts, lncRNAs are usually transcribed by RNA polymerase II and play a role through 5′ end capping, RNA splicing, and polyadenylation. It has been determined that there are thousands of lncRNAs in the human genome, which significantly exceed the number of protein coding genes. Since lncRNA usually lacks significant sequence characteristics and  [11]. At present, lncRNA classification [4] is based primarily on a genome position relative to the nearby protein encoding gene. Specifically, it can be divided into the following categories: intronic lncRNA: lncRNA located in the intron region of the protein coding gene; intergenic lncRNA: lncRNA that does not overlap with any protein coding gene; bidirectional lncRNA: pairing [5] lncRNA/mRNA through bidirectional transcription of the shared promoter region; and sense lncRNA (sense lncRNA) or antisense lncRNA (antisense lncRNA): lncRNA that overlaps the positive chain or antisense chain of another protein encoding gene. Most lncRNA expressions have a high tissue specificity and are adjusted by many physiological and pathological conditions. The disorders of lncRNA expression are related to many human diseases, including tumors [12]. Studies have shown that lncRNA regulates a series of biological processes such as cell proliferation, differentiation, survival, and migration and exerts biological functions by interaction with other cell midmolecules. For example, lncRNA acts as a guide for protein DNA interaction or an enhancer of adjacent genes by binding to chromatin and DNA. lncRNA acts as a scaffold for protein-protein interaction by interacting with proteins and can attract proteins. lncRNA [13] can not only regulate mRNA splicing, RNA stability, and protein translation by combining with mRNA or other NC RNAs but also "exchange information" with other small RNAs. For example, miRNA participates in the change of biological function through the mechanism of competitive endogenic RNA (CE RNA). Therefore, lncRNA, miRNA, and RNA encoding proteins may form a complex regulatory network [14], which interact with each other and regulate gene expression [15] by epigenetic, transcriptional, and posttranscriptional regulation and other genes through gene imprinting, chromatin remodeling, cell cycle regulation, splicing regulation, and so on and play a role in regulating various biological functions. With the in-depth study of tumor pathogenesis, lncRNA plays an important role in the occurrence and development of a variety of tumors. A large number of studies have shown that pvt1, as an intergenic lncRNA, is highly expressed in a variety of tumors such as liver cancer, gastric cancer, and non-small-cell lung cancer, plays the role of oncogene, and is related to the prognosis of patients [16]. It was found that there were many abnormally expressed lncRNAs in ALL. Pvt1 [17] is one of the lncRNAs that is upregulated in ALL cells. It is located on chromosome 8q24 with a total length of 670 bp and is closely related to the oncogene c-myc. Overexpression of c-myc can promote the proliferation of tumor cells [18]. Zeng et al. found that the expression of pvt1 in peripheral blood cells of patients with acute promyelocytic leukemia was significantly upregulated. Further analysis of the effect of all trans retinoic acid (ATRA) on the expression of c-myc found that the expression of c-myc and pvt1 decreased significantly during the differentiation and cell cycle arrest of acute promyelocytic leukemia induced by ATRA. Knockdown of c-myc in the acute promyelocytic leukemia cell line NB4 could lead to downregulation of pvt1. The expression of pvt1 in acute promyelocytic leukemia cells transfected with pvt1 interfering RNA decreased, resulting in the inhibition of myc protein expression. It was confirmed that the upregulation of pvt1 expression in acute promyelocytic leukemia cells can promote the proliferation of tumor cells [19]. Studies at home and abroad have found that the expression of pvt1 is    3 Computational and Mathematical Methods in Medicine upregulated in patients with chronic myeloid leukemia, and studies have shown that [20] pvt1 silencing leads to cell cycle arrest by negatively regulating the expression of cell cycledependent kinase inhibitors p15 and p16, so as to inhibit the growth of tumor cells. However, there are few reports on the role and related mechanism of lncRNA-pvt1 in childhood ALL. In this study, RT-PCR was used to analyze and detect pvt1 expression in bone marrow of ALL patients. At the same time, sh-pvt1 and its blank control plasmid were transfected into Jurkat cells. The MTT assay and flow cytometry showed that silencing pvt1 inhibited Jurkat cell proliferation (Figures 1-4).
In conclusion, pvt1, as an intergenic lncRNA, is involved in the occurrence of multiple tumors and is highly expressed in both acute myeloid leukemia and chronic myelogenous leukemia. Silencing pvt1 expression can inhibit the occurrence of ALL. Since lncRNA PVT1 was involved in the regulation of DNA, RNA, and protein levels, the Luciferase assay, RIP, CHIP, EMSA, and in vitro binding assay were used to further verify the direct binding relationship between proteins, DNA, and RNA of different genes.

Data Availability
No data were used to support this study.

Conflicts of Interest
The authors declare that they have no conflicts of interest.